uberAgent, a Windows performance and user experience monitoring agent for Splunk, has been supporting GPU usage monitoring for a while now. It can tell you GPU compute and memory usage per machine and per individual process, as well as document which GPU model is built into which machine.
For more information:
Product homepage: http://helgeklein.com/uberagent-for-splunk/
Blog article that shows how to use uberAgent’s data to determine battery life and GPU usage during video playback: http://helgeklein.com/blog/2014/02/gpu-acceleration-battery-life-video-playback-windows-8-1/
Disclaimer: I am the owner of the company that creates uberAgent.